Method of treating a petroleum fraction using molecular sieve aluminosilicate selective adsorbents



March 12, 1963 MET Filed May 18, 1959 H. V. HESS ET AIL HOD OF' TREATINGA PETROLEUM FRACTION USING MOLECULAR SIEVE ALUMINO-SILICATE SELECTIVEADSORBENTS Fifa ra Peron/ns@ ae Cam/mme 2 SheetsO-Sheet 1 ny Cam/:km0He'obacr I ,PE/rayman' Mam/cr ppg-5 aF 5799/6447' cfm/N #wen/means March12, 1963 HESS ET AL 3,081,255 METHOD OE TREATING A PETROLEUM FRACTIONUSING MOLECULAR SIEVE ALUMINO-SILICATE SELECTIVE AOSORBENTS Filed May18, 1959 2 Sheets-Sheet United States Patent 3,081,255 METHGD F TREATlNGA PETROLEUM FRAC- TION USING MOLECULAR SIEVE ALUMINO- SlLlCATE SELECTVEADSORBENTS Howard V. Hess, Glenham, and Edward R. Christensen,Wappingers Falls, NY., assignors to Texaco Inc., New York, N.Y., acorporation of Delaware Filed May 18, 1959, Ser. No. 813,707 Claims.(Cl. 208-88) This invention relates to a method of treating petroleumfractions. More particularly, this invention relates to an improvedhydrocarbon conversion process. In accordance with one embodiment thisinvention relates to the treatment of petroleum fractions in the naphthaor gasoline boiling range to improve their quality. Still `moreparticularly, this invention is directed to the treatment of petroleumfractions containing straight cham hydrocarbons and non-straight chainhydrocarbons, especially naphtha stocks wherein the amount of straightchain hydrocarbons is substantial, i.e., in the range 3-30% by volumeand higher.

Various converting and catalytic reforming processes have been proposedfor the treatment of naphtha stocks to produce a high quality, highoctane motor fuel. These processes call for the vapor phase treatment ofpetroleum fractions in the gasoline boiling range by contact with anactive converting catalyst such as a platinum-containing catalyst, achromia-alumina catalyst, a molybdenaalumina catalyst or the like.During treatment of these selected petroleum fractions, a number ofreactions take place substantially simultaneously. For example, in acatalytic reforming operation employing a platinum-containing catalystin contact with a naphtha fraction containing aromatics, naphthenes,isoparains and n-parafns, dehydrogenation of the naphthenes to aromaticsoccurs. Substantially at the same time isomerization and dehydrogenationof the paraliinic hydrocarbons take place. Additionally, under theseconditions aromatization or dehydrocyclization of the paratlinichydrocarbons also takes place. Concurrently with these reactions,particularly under the more severe treating or conversion conditions, acertain amount of cracking and gas formation (C4= and lighter) takesplace together with deposition of carbon upon the catalyst therebyresulting in a reduction in the recoverable yield of the more valuablenormally liquid hydrocarbons. Cracking, as evidenced by gas formationand carbon deposition, is particularly noticeable when the aforesaidconversion or catalytic reforming reactions are carried out under themore severe catalytic reforming conditions in order to produce a highoctane motor fuel or motor fuel component.

The platinum-containing treating catalysts employed in present daycommercial catalytic reforming operations are expensive. Some of theseplatinum-containing catalysts are regenerable and some arenon-regenerable. An important factor in the determination of the usefullife of a treating or a catalytic reforming catalyst, particularly aplatinum-containing catalyst, is the amount of carbon deposited or laiddown upon a catalyst. Carbon deposition in turn is usually governed ordependent upon the severity of the converting or reforming conditions inwhich the catalyst is employed. The replacement of a spent treatingcatalyst, particularly a platinum-containing catalyst, is expensive.Moreover, the regeneration of a `spent regenerable catalyst is anexpensive operation and time consuming, all the more so in a refineryoperation when for purposes of regeneration it is necessary to take acatalyst case off stream for catalyst regeneration.

Accordingly, it is an object of this invention to provide 3,081,255Patented Mar. 12, 1963 ICC an improved process for treating petroleumfractions containing straight chain hydrocarbons.

It is another object of this invention to provide a ilexible petroleumconverting operation which is capable of handling a wide variety ofpetroleum fractions containing straight chain hydrocarbons andnon-straight chain hydrocarbons.

Still another object of this invention is to provide a treating processwherein the useful on-stream life of a treating catalyst, especially aplatinum-containing catalyst, is substantially increased, particularlywhen compared with the useful catalyst life of the same catalystemployed in the same catalytic conversion operation in the conventionalmanner to produce a petroleum fraction or gasoline component havingthesame octane number as produced by the combination treating process inaccordance with -this invention.

Yet another object of this invention is to provide a combinationtreating operation employing a catalytic converting or catalyticreforming operation for the production of'a high octane motor fuel nototherwise obtainable save at the expense of a prohibitively shortenedcatalyst life.

Yet another object of this invention is to provide a combination processfor increasing the yield of a given high octane number motor fuelobtainable from a given naphtha fraction as compared to the yieldobtainable by employing a conventional operation.

Yet another object of this invention is to provide a petroleum productparticularly useful as a motor fuel.

Still another object of this invention is to provide a process for theproduction of a petroleum product particularly useful as a jet fuel.

In at least one embodiment of this invention at least one of theforegoing objects will be achieved.

How these and other objects in this invention are achieved will becomeapparent with reference to the accompanying disclosure and drawingwherein:

FIG. 1 is a block ow diagram broadly outlining the process of thisinvention, and

FIG. 2 is a schematic flow diagram illustrating various embodiments ofthe practice of this invention.

In accordance with this invention we have provided an improved processfor treating or converting a petroleum fraction containing straightchain hydrocarbons and nonstraight chain hydrocarbons which comprisessubjecting the petroleum fraction to a treating or converting operation,such as a catalytic reforming or isomerization operation, to produce apetroleum fraction of improved quality, such as an improved or higheroctane product, and subjecting the resulting improved petroleum fractionto Contact with a solid absorbent which selectively adsorbs straightchain hydrocarbons to the substantial exclusion of non-straight chainhydrocarbons, to adsorb straight chain hydrocarbons from said fraction,thereby producing a further improved petroleum fraction. The practice ofthis i11- vention is particularly applicable to any petroleum fractionsuitable for use in a catalytic reforming or isomerization operation orsuitable for the production of aromatics or improved naphthas or motorfuels in the gasoline boiling range, provided, of course, said petroleumfraction contains straight chain hydrocarbons and non-straight chainhydrocarbons.

By straight chain hydrocarbons is meant any aliphatic Hydrocarbon type:

practice of this invention. plated that selective adsorbents having theproperty of selectively adsorbing straight chain hydrocarbons to thesubstantial exclusion of non-straight chain hydrocarbons in the mannerof a molecular sieve may be obtained by suitable treatment of variousoxide gels, especially metal oxide gels of the polyvalent amphotericmetal Oxides. 5,.-

rg A petroleum fraction suitable for use in the practice of thisinvention might have an initial boiling point in the range 50-300 F. andan end point in a range 2(l0475 F., more or less. Furthermore, apetroleum fraction suitable for use in the practice of this inventioncontains both straight chain and non-straight chain hydrocarbons andmight have the following composition.

Percent by volume Naphthenes 0-75 Aromatics 0-50 10 Parafns (includingnormal parains and isoparaflins) 3-90 Unsaturates (including normaloleiins and isoolens, etc.) 0-50 15 The straight chain hydrocarbons,e.g., the n-paran content of petroleum fractions suitable for use in thepractice of this invention is frequently in the range 3-50% by volume.are applicable to the practice of this invention are a wide boilingstraight run naphtha, a light straight run naphtha, a heavy straight runnaphtha, a catalytic cracked naphtha, a thermally cracked or thermallyreformed naphtha. This invention, however, is particularly applicable tothe treatment of catalytic reformates in the naphtha boiling range.

Typical refinery stocks or fractions which Any solid adsorbent whichselectively adsorbs straight chain hydrocarbons to the substantialexclusion of nonstraight chain hydrocarbons can be employed in thepractice of this invention. It is preferred, however, to employ as theadsorbent certain natural or synthetic zeolites or alumino-silicatessuch as a calcium alumino-silicate which exhibit the property of amolecular sieve, that is, adsorbents made up of porous matter orcrystals wherein the pores are of molecular dimension and are of uniformsize. A particularly suitable solid molecular sieve adsorbent for theadsorption of straight chain hydrocarbons to the substantial exclusionof non-straight chain hydrocarbons is a calcium alumino-silicate,apparently actually a sodium calcium alumino-silicate, having a poresize or diameter of about 5 Angstrom units, a pore size sufficient toadmit straight chain hydrocarbons, such as the n-parains, to thesubstantial exclusion of the non-straight chain hydrocarbons, such asthe naphthenic, aromatic and the isoparans and iso-olefinichydrocarbons, e.g. isobutane and higher. cially available in varioussizes such as 1,/16 or 1A" diameter pellets as well as in a finelydivided powder form.

This particular selective adsorbent is commer- Other selectiveadsorbents may be employed in the For example, it is contem- Othersuitable selective adsorbents are known and include the synthetic andnatural zeolites which, when dehydrated, may be described as crystallinezeolites having a rigid three dimensional anionic network and havinginterstitial dimensions suliciently large to permit the entry of andadsorb straight chain hydrocarbons but sufliciently small to exclude thenonstraight chain hydrocarbons. The naturally occurring zeolite,chabazite, exhibits such desirable properties. ring zeolite is analciteNaAlSi2O6-H2O which, when dehydrated, and when all or part of the sodiumis replaced by an alkaline earth metal, such as calcium, yields amaterial which may be represented `by the formula (Ca,Na)Al2Si.,O12.2I-I2O and which after suitable conditioning will adsorbstraight chain hydrocarbons to the substantial exclusion of non-straightchain hydrocarbons. Naturally occurring or synthetically preparedphacolite, gmelinite, harmotome and the like, or suitable modificationsof these products by base exchange, are also applicablein the practiceof this invention.

Another suitable naturally occur- Other solid adsorbents whichselectively adsorb straight chain hydrocarbons such as n-parafns and then-olens to the substantial exclusion of the non-straight chainhydrocarbons, including the aromatic and naphthenic hydrocarbons, areknown.

Referring now to FG. l of the drawing which sets forth in a block flowdiagram various embodiments of the practice of this invention, a freshfeed petroleum fraction which may have a wide or narrow boiling range,containing straight chain hydrocarbons (n-paraflins and/or n-olens) inadmixture with non-straight chain hydrocarbons (aromatic and/ornaphthenic and/or isoparaffinic and/or isooleiinic hydrocarbons), issupplied from a suitable source to a suitable feed fractionation and/orpreparation unit. Should the fresh feed contain substantial amounts ofundesirable polar or polarizable compounds such as sulphur-containingcompounds, oxygenated hydrocarbons, nitrogen-containing compounds andthe like, it is sometimes desirable, although not necessary, to removethese materials from the feed prior to the special subsequent treatmentin accordance with this invention. The removal of these polar orpolarizable materials may be accomplished by solvent extraction,extractive distillation, hydrogenation, dehydrogenation, acid or causticwashing and the like or by any suitable combination thereof. Processesfor removal of or neutralization of the abovementioned polar andpolarizable materials in a petroleum fraction are well known.

Advantageously, preferably prior to feed preparation, the fresh feed issubjected to fractionation to produce a petroleum fraction having theboiling point range most suitable for subsequent treatment in accordancewith this invention. If the fresh feed contains components which have aboiling point below about F., it is usually desirable to removesubstantially all of these feed components. Hydrocarbons which have aboiling point below 100 F. are n-butane, isobutane, isopentane andneopentane, all of which possess a rather high octane number and forthis reason alone would be desirable components in a motor fuel orgasoline. Normal pentane, having a boiling point of about 97 F.,however, has a lower octane number (about 61) and accordingly itspresence in a motor fuel is less desirable.

The removal of these low boiling hydrocarbons is desirable since theselow boiling hydrocarbons are refractory and do not readily undergocatalytic reforming. When these low boiling hydrocarbons are passed to acatalytic reforming operation they pass through substantially unchangedand in effect act as a diluent. Accordingly, the low boiling, C5 or C4and lighter, hydrocarbons are advantageously fractionated from the feedundergoing treatment in accordance with this invention. All or a portionof these low boiling hydrocarbons, however, may aclvantageously beblended back into the final treated petroleum fraction or otherwiseemployed, e.g., as a desorbing agent, in the practice of this invention.

Following the feed fractionation and/or preparation operations asindicated in FIG. l, the naphtha feed is sent to a conversion operation,such as a catalytic reformer, which might also be an isomerization unit,wherein it is contacted with an active reforming catalyst underreforming conditions of temperature land pressure to upgrade the feedinto a converted product or reformate as an improved motor fuel or highoctane motor fuel component.

Various converting and catalytic reforming or isomerizing operationsparticularly suitable for upgrading a petroleum fraction in a naphthaboiling range may be employed in the combination treating process inaccordance with this invention. Generally, reforming or isomerizationprocesses, the words reforming and isomerizing being used hereininterchangeably, may be described as processes for upgrading relativelylow octane naphthas or petroleum fractions in the gasoline boiling rangeto high octane motor gasolines, or as processes for producing highoctane motor fuel components from selective naphthas or petroleumfractions, or as processes for producing a high yield of aromatichydrocarbons or high octane motor fuel components.

These catalytic reforming operations may be carried out by employing axed bed of catalyst, a moving bed of 'catalyst or a uidized catalyst, orany combination thereof, `and are generally operated at a temperature inthe range 40G-1000 F., more or less, and a pressure in the range 25-900p.s.i.g., more or less, depending upon the severity or extent ofreforming desired or the reforming catalyst employed or the quality orcomposition of the petroleum fraction undergoing reforming and/or theproduct desired. Various catalysts suitable for reforming hydrocarbonsmay be employed, eg., platinum-containing catalysts, molybdena-aluminacatalysts, chromiaalumina catalysts and cobalt-molybdate catalysts; theparticular reforming or isomerizing process is sometimes adequatelydefined merely by ydescribing the particular catalyst employed therein.As a result of the reforming operation, there is produced and recovereda reformate having improved qualities as a motor fuel.

Depending upon the composition of the fresh vfeed other convertingprocesses, in place of catalytic reforming, may be employed, c g.thermal cracking, thermal reforming (essentially non-catalyticprocesses), etc., particularly when the fresh feed contains asubstantial amount, in the range -50 and higher percent by volumestraight chain hydrocarbons.

The effluent from the reforming or converting operation is treated toseparate the normally gaseous materials therefrom, e.g. hydrogen,methane, ethane, propane and C4 hydrocarbons. At least a portion of theseparated and recovered hydrogen is usually desirably recycled to thereforming or converting operation.

The remaining normally liquid components of the effluent are thencontacted with the solid selective adsorbent material in powdered,beaded, microspheroidal, granular or pelleted form to selectively adsorbthe straight chain hydrocarbons therefrom. Although it is preferred toremove substantially all of the straight chain hydrocarbons from theeiiiuent it is realized that it is not necessary in the practice of thisinvention to adsorb or separate all of the straight chain hydrocarbons.The extent or degree of straight chain hydrocarbon removal, especiallyfor octane number improvement, in order to produce a high octanegasoline is governed by various factors, economic and otherwise,including capacity of the available equipment, the quality desired inthe finished treated product, yield considerations, the composition ofthe effluent and the like.

The effluent undergoing treatment for the removal of the straight chainhydrocarbons therefrom may be present either in the liquid phase or in agas or vapor phase. The capacity of the solid adsorbent material as aselective adsorbent for straight chain hydrocarbons is substantiallyunaffected by the phase condition of the material to be treated(reformer efuent) in contact therewith, provided sufcient time isallowed to substantially saturate the adsorbent. Contact of the eflluentwith the solid adsorbent may be effected by any suitable means foreffecting gassolid or liquid-solid contacting. For example, in contactwith the reformer effluent the selective adsorbent may be maintained asa fixed bed, a moving bed or a fluid bed.

When liquid phase contacting is carried out for the removal of thestraight chain hydrocarbons from the eiiuent, it is preferred to carryout the adsorption operation at a temperature in a range 50-500" F. orhigher, sufficient pressure being applied, if necessary, to maintain theeffluent in the liquid phase. In vapor phase adsorption it is preferredto carry out the adsorption operation at a temperature at leastsufficient to maintain substantially all of the eiuent undergoingtreatment in the vapor phase, such as a temperature in the range 30D-700F. or higher. Satisfactory liquid phase or vapor phase adsorptionoperations have been carried out at temperatures in the range ZOO-650 F.

The effluent undergoing treatment is maintained in contact Iwith theselective adsorbent until substantially all of the straight chainhydrocarbons have been removed therefrom, or until the selectiveadsorbent has become substantially saturated with respect to straightchain hydrocarbons. When the adsorbent is substantially saturated, sothat straight chain hydrocarbon adsorption is no longer possible, thepetroleum fraction or effluent undergoing treatment is contacted withadditional fresh or regenerated adsorbent.

The straight chain hydrocarbons are desorbed from the adsorbent, therebyregenerating the adsorbent, by contacting the adsorbent with a strippingmedium which displaces, purges, desorbs or sweeps out the adsorbedstraight chain hydrocarbons from within the pores of the selectiveadsorbent. Preferably the stripping medium is readily separable, as bydistillation, from the desorbed straight chain hydrocarbons. Exemplaryof a suitable stripping medium are nitrogen, methane, hydrogen, ue gas,carbon dioxide, substantially dry natural gas and the normally gaseoushydrocarbons such as ethane, propane, n-butane and isobutane. Liquidsare also useful as a stripping medium, such as the liquefied normallygaseous hydrocarbons, including propane, n-butane, isobutane, n-pentane,isopentane and higher and lower molecular weight hydrocarbons ormixtures thereof. Desirably, the molecules of the stripping mediumthereof are suiciently small to enter the pores of the adsorbent.

The desorption operation may be carried out at any suitable temperature,higher or lower, or, if desired, isothermal With respect to theadsorption operation. Similarly the desorption operation may be carriedout at a pressure greater than or less than or isobaric with respect tothe adsorption operation. A desorption temperature in the range ZOO-090F. has been found to be satisfactory and the desorption temperature maybe in the range 10U-300 degrees Fahrenheit higher than the adsorptiontemperature, such as a temperature in the range 30G-700 F.

After the straight chain hydrocarbons have been desorbed, the straightchain hydrocarbons are recovered and, if desired, are subjected to asuitable conversion operation such as catalytic reforming orisomerization, or thermal cracking in order to upgrade the desorbedstraight chain hydrocarbons into more valuable materials, e.g. normalparaflins to normal oleins and/ or to their corresponding branchedcha-in isomers. The resulting converted product can be directly blendedwith the straight chain hydrocarbon-free eiiluent from the adsorber or,if desired, may be contacted with selective adsorbent to remove thestraight chain hydrocarbons therefrom and the remaining straight chainhydrocarbon-free converted product blended with the above-mentionedetliuent. Also, the desorbed straight chain hydrocarbons may beseparately recovered and utilized as such, as an industrial solvent, jetfuel, etc.

In FIG. 2 of the drawing there are schematically illustrated variousembodiments of the practice of this invention. Referring now in greaterdetail to FIG. 2 a fresh feed petroleum fraction, such as a petroleumfraction in the naphtha boiling range, from a source not shown, issubjected to fractionation and/ or preparation by feed preparation unit11. During fractionation and/ or preparation of the fresh feed thereinto yield a petroleum fraction having a suitable boiling point range forsubsequent treating in accordance With this invention, the lightercomponents of the fresh feed, such as the hydrocarbons having amolecular weight in the range C5 and lower, especially substantially allof the isopentane and butane contained in the fresh feed, areadvantageously removed overhead as a separate fraction via line 12. Theremaining fresh feed, substantially free of C5 and lower molecularweight hydrocarbons, and having the desired boiling point range, such asa boiling range in the range 15G-450 F., is subjected to a feedpreparation operation which might involve a mild hydrogenation orhydrogen refining operation to saturate the unsaturated hydrocarbonstherein, for removal of the more polar compounds therefrom, eg.sulfur-containing compounds and the like. Application of theabove-described operations of kfresh feed fractionation and/ orpreparation to a straight run naphtha fraction would produce a heavystraight run naphtha fraction which might have the composition set forthin accompanying Table I. A naphtha fraction possessing these propertieswould be suitable for subsequent treatment in accordance with thisFollowing suitable feed fractionation and preparation treatment theprepared feed issues from unit 11 via line 13 into heater 14 where it isbrought up to a sufliciently high temperature, such as a temperature inthe range 400- 1000 F., for introduction via line 15 into catalyticreforming unit 16. Catalytic reforming unit 16 is suitably provided withan active reforming catalyst such as a platinumcontaining catalyst whichmay be regenerable or nonregenerable, or a chromia-alumina catalyst or amolybdena-alumina catalyst or a cobalt-molybdate catalyst. Typicaloperating conditions for catalytic reformer 16 when employing 4aplatinum-containing catalyst are as follows: inlet temperature 875 F.,pressure 250 p.s.i.g., space velocity 3 v./hr./v. with a recycle of 8000cu. ft./ bbl. of prepared feed of a gas containing at least about 90 molpercent hydrogen. T wo or more of catalytic reforming units 16 may beemployed in series or in parallel.

Within catalytic reforming unit 16 hydrocarbon components present in thetreated feed are upgraded into higher octane hydrocarbons with aresulting net production of hydrogen. For example, the naphthenichydrocarbons are dehydrogenated to form a corresponding aromatichydrocarbon. Substantially simultaneously therewith the isoparainic andnormal paratiinic hydrocarbons undergo isomerization, dehydrocyclizationand a certain amount of cracking with resulting gas formation (C4 andlower molecular weight hydrocarbons) depending upon the severity of thereforming operation. In any event the effluent issuing from reformer 16has an increased aromatic hydrocarbon content and/or improved qualitiesas a motor fuel and/ or a higher octane rating, as compared to the feedsupplied to reforming unit 16.

The effluent issuing from reforming unit 16 Via line 19 is passed to agas-liquid separator 21 wherein the hydrogen produced during thereforming operation is separated. At least a portion of this separatedhydrogen is usually recycled via line 20 to reformer 16 t0 provide thedesired hydrogen therein. The remaining reformer eluent or reformate isadvantageously passed from gas-liquid separator 21 via line 22 intofractionator 23 wherein an overhead fraction comprising substantiallyall of the C and/ or C., and lighter hydrocarbons are removed overheadas a separate fraction via line 24. The remaining higher molecularweight, higher boiling effluent, comprising substantially all of thenormally liquid hydrocarbons in the reformer euent, are passed via line25 to heater 26 wherein the eluent, if desired, is heated to a suitabletemperature for introduction into adsorber 29. The resulting effluent isintroduced from heater 26 into adsorber 29 by rated with respect tostraight means of line 30. If heater 26 is unnecessary, especially if itis desired to carry out liquid phase adsorption, it may be bypassed vialine 17.

If desired, the reformer effluent in fractionator 23, after removal ofthe C5 and/or C4 and lighter hydrocarbons is further fractionated toprocure a side cut via line 28 :having a boiling point not greater thanabout 250 F. It has been observed that the remaining higher boilingfraction, such as a reformate having a boiling point range in the rangeZ50-450 F., more or less, is less susceptible to upgrading as regardsoctane number increase by subsequent treatment in accordance with thisinvention. This higher boiling fraction accordingly may be separatelyremoved from fractionator 23 as a bottoms fraction via lines 25 and 27for subsequent blending, by means not shown, with the blended product inline 61.

Adsorber 29 is provided with a fixed bed of solid particle molecularsieve selective adsorbent. As disclosed suitable adsorbents for straightchain hydrocarbons are the alkaline earth metal alumina-silicates, moreparticularly the calcium alumino-silicates, e.g. sodium calciumalumino-silicate. The adsorber 29 is operated at a temperature such thatsubstantially all of the straif'ht chain hydrocarbons, such as thenormal paratins in the effluent introduced into adsorber 29 via line 30in the gaseous or liquid phase, are adsorbed by the adsorbent materialtherein with the result that there issues from the bottom of adsorber 29Via line 31 in the gaseous or liquid phase a treated or finishedreformate fraction substantially free of straight chain hydrocarbons.

The adsorption conditions within adsorber 29 are to some extentdependent upon the composition of the reformate or reformate fractionundergoing treatment or finishing therein, eg., the greater the amountof straight chain hydrocarbons the longer the adsorption or finishingperiod required to effect substantially complete adsorption of thestraight chain hydrocarbons. Removal of the straight chain hydrocarbons,especially the straight chain parafinic hydrocarbons, is desirable sincethese hydrocarbons possess a very low octane number. For example, normalhexane has an octane number of 24, normal heptane an octane number of 0,normal octane an octane number of -17. The removal of the normal parainsfrom the reformer effluent therefore is desirable when it is desired toproduce a high octane motor fuel. The branched chain hydrocarbons, suchas the branched chain isomeric parafiinic hydrocarbons, in a motor fuelare not undesirable since branched chain hydrocarbons in general possessa relatively high octane number. For example, isohexane has an octanenumber of about 73.

Processing or finishing periods for the eluent undergoing treatment nadsorber 29 in the range 2 minutes up to about 11/2-2 hours atthroughputs in the range 1A v./hr./v. up to about 20 v./hr./v. aresatisfactory and suitable in order to effect the desired removal of thestraight chain hydrocarbons or before the adsorbent material withinadsorber 29 is substantially lsaturated with straight chainhydrocarbons. The nished eflluent ssuing from adsorber 29 via line 31may be withdrawn as a separate reformate product via line 32 or blendedwith additional hydrocarbons in a manner to be described hereinafter.

After a suitable period of time and when the adsorbent material withinadsorber 29 becomes substantially satuchain hydrocarbons regeneration ofthe adsorbent by desorption of the straight chain hydrocarbons therefrombecomes necessary. The straight chain hydrocarbons are desorbed from theadsorbent by contacting the adsorbent with a desorbing fluid orstripping medium such as nitrogen, methane, natural gas, flue gas,carbon dioxide, hydrogen, gaseous hydrocarbons and gaseous or liquefiednormally gaseous hydrocarbons, etc. The stripping medium is introducedinto adsorber 29 via line 33 or by multi-point injection via lines 33a,having been supplied from suitable sources via line 35. Hydrogen, ifemployed as a stripping medium, is advantageously supplied lfromgas-liquid separator 21 via lines 20, 36 and 39 and if gaseous andliqueed C3 and C4 hydrocarbons and the like are employed as strippingmedium these materials may be supplied from fractionator 23 via lines24, 59, 60, 37 and 33.

The desorption operation, as previously stated, may be carried out atsubstantially the same temperature as the adsorption operation. Althoughliquid phase adsorption and desorption are suitable and the variouscombinations of liquid and gaseous adsorption and desorption are useful,it is sometimes desirable to employ a desorption temperature suicient tomaintain the materials being treated or desorbed in the vapor phase,e.g. temperature in the range 30D-700 F. during adsorption and atemperature in the range 40G-900 F. during desorption. Usually in theseinstances the desorption temperature is about 100-300 degrees Fahrenheithigher than the adsorption temperature, generally in the range SOO-100W7F. As a general rule the desorption temperature should be such that the-adsorbed straight chain hydrocarbons are relatively quickly desorbedwithout at the same time causing destruction of the adsorbent ordecomposition or cracking of the adsorbed-deso-rbed hydrocarbons. Thedesorbed straight chain hydrocarbons together with the accompanyingstripping medium issue from adsorber 29 via line 40 and are introducedinto gas-liquid separator 41. When a normally gaseous stripping medium,such as hydrogen, iiue gas, nitrogen and the like is employed a-s thestripping medium the separation of these normally gaseous materials andthe desorbed straight chain hydrocarbons is effected Within separator41, the normally gaseous stripping medium being removed via -line 42 andrecovered for further use as a stripping medium by means not shown andthe straight chain hydrocarbons are removed via line 43.

The -desorbed straight chain hydrocarbons issuing from separator `41 vialine 43 may be recovered as a separate product via line 44 or sen-t to asubsequent conversion operation, to be described, via line 45. Advan-Itageously when hydrogen is employed as a strip ing medium and when theaforesaid subsequent conversion operation is -a catalytic conversionoperati-on or isomeriza- `tion Operation or the like wherein thepresence of hydrogen during the conversion of the desorbed straightchain hydrocarbons is desirable, the vaporized desorbed straight chainhydrocarbons together with the hydrogen stripping medium are recycledwithin adsorber 29 via lines 40, 46 and 47, gas-liquid separa-tor beingby-passed, until the desired hydrocarbon concentration has been reachedat which time a portion of the hydrogen and hydrocarbon mixture in line46 is introduced into line 45, heater 49 and line 50 into converter 51.Fresh hydrogen m-ay be supplied as additional stripping medium `fromsepara-tor 21 via lines 29, 36, 39 and 33 and then, as indicated,eventually into line 45 via lines 40 and 46, by-passing the gas-liquidseparator 41. The desorbed straight chain hydrocarbons move Via line 45to heater 49 where they are brought up to the desired conversiontemperature and introduced via line 50 into converterhydrocarbon-containing gas.

51 wherein the desorbed straight chain hydrocarbons are converted intohigher octane or improved motor fuel components. If desired, asindicated in FIG. 2 the desorption effluent containing hydrogen andstraight chain hydrocarbons may be recycled :to reformer 16 via lines47, 17 and 15.

The conversion operation carried out Within converter 51 may be thermalcracking, thermal reforming, catalytic cracking, catalytic reforming,isomerization and the like, depending upon .the properties andcomposition of the desorbed straight chain hydrocarbons. Preferably theconversion operation within converter 51 is an isomeriz-ation operationemploying an isomerization catalyst such as a platinum-containingcatalyst. The upgraded effluent issuing from converter 51 via line 52,now possessing a higher -octane number and now containing straight chainhydrocarbons and non-straight chain hydrocarbons, may be removed as aseparate converted product via line 53, or blended with thesubstantially straight chain hydrocarbon-free eiiiuent issuing fromadsorber 29 via line 31 by means of line 54 or all or a portion of theefiiuent from converter 51 may be returned via lines 52 and 55 and line22 .to fractionator 23 and adsorber 29 for additional treatment aspreviously described.

'Ihe overhead fractions in lines 12 and 24 containing C5 and/ or C4 andlighter hydrocarbons, from feed preparation unit 11 and fractionator 23,respectively, preferably containing substantially all of the isopentaneand the C4 hydrocarbons present in the fresh feed and the effluentissuing from catalytic reformer 16, are combined by lines 5'6 and 59,respectively, into line 60 for blending with the combinedadsorber-converter effluent in line 31 and are removed as a separatefinished blended converted reformate product via line 61. If desired,all or a portion of the combined overhead fractions in line 60 m-ay bepas-sed via line 62 -to a liquefied petroleum gas recovery plant.Further, if desired those normally gaseous hydrocarbons, C3, C4, etc.,recovered via lines 12 and 24 may be employed via lines 60, 37 and 33Ito desorb the adsorbed straight chain hydrocarbons.

Exemplary of the advantages obtainable in the practice of this inventionas applied to a 20,00() bbl. a day charge catalytic reforming unitemploying a platinumcontaining catalyst, it has been determined `thatwhen such a unit is operated in the conventional manner, including amild hydrogenation treatment of the feed thereto, to produce a catalyticreformed gasoline having an octane number of about 93 there `is produced16,140 barrels per day of -a debutanized gasoline having a research-octane number clear of 92.9. Additionally there is produced a hydrogenand hydrocarbon-containing fuel gas in an amount equal to 15,003 MMstandard cu. ft. This amount of gas represents an actual loss ofhydrocarbons. However, when operating in accordance with the practiceo-f this invention employing -in combination a catalytic reforming unitfollowed by selective finishing of the resulting reformate to removesubstantially all the straight chain hydrocarbons therefrom, `it wasdetermined that the reforming unit cou-ld be operated at a lesser degreeof severity, as indicated by the recovery of 17,440 barrels per day ofdebutanized ygasoline and the recovery of a smaller amount of hydrogenand The increased recovery of debutanized gasoline amounts to about an8% by volume increase over the conventional opera-tion.

'Ihe recovered debutanized catalytic reformed gasoline amounting to17,440 barrels per day is then treated in the manner of the inventiondescribed herein with a selective adsorbent for the removal of straightchain hydrocarbons therefrom and there is produced 16,272 barrels perday of catalytic reformed gasoline having a clear research octane numberof 92.9 together with 1168 barrels per day of straight chainhydrocarbons which may be recovered and employed as such as a solvent orsubjected to an isomerizattion or catalytic reforming operation toproduce additional high octane motor fuel or ernployed per se as a jetfuel. The advantages of employing the practice of this invention are anincreased recovery of hi-gh octane gasoline since, as indicatedhereinabove, less of the treated hydrocarbons are converted to =butanesand lighter hydrocarbons. Additionally since the platforming operationoperated in the combination treating process in accordance with` thisinvention is carried out under less severe co-nditions the usefulcatalyst life is extended at least twofold, days vs. 'Z0 days.

Further indicative of the advantages obtainable in the practice of thisinvention an 85.9 CFRR (clear) catalytic reformed gasoline (catalyticreformate) was upgraded in 'accordance with the practice of thisinvention by vapor phase contact with Ka molecular sieve selectiveadsorbent l l for the removal of the straight chain hydrocarbonstherefrom. The results are summarized below in Table II:

TABLE Il Adsorption temperature, F:

rPhe above operations were carried out employing a finishing oradsorption time of about thirty minutes, a space velocity of about 1v./hr./v. and a desorption or regeneration temperature, followingadsorption, of about 700 F. employing natural gas as the strippingmedium.

Further indicative of the practice of this invention a catalyticreformed gasoline having a research octane number clear of 86.8 wasupgraded by vapor phase contact with a solid molecular sieve selectiveadsorbent for straight chain hydrocarbons employing a space velocity ofabout 1 v./hr./v., for the removal of straight chain hydrocarbonstherefrom. The adsorption and desorption was carried out at varioustemperatures, desorption being effected by natural gas comprisingsubstantially one methane. The operating conditions and results obtainedare set forth in Table III.

TABLE III Adsorption Desorption Product Octane Run No. Research,

Temp., Time, Temp., Time, Clear F. Min. F. Mn.

Since the straight chain hydrocarbons removed from the efliuentundergoing finishing, such as a catalytic reformer efliuent, represent asubstantial fraction thereof it is desirable in accordance with thepractice of this invention to upgrade the straight chain hydrocarbonswith respect to octane number or otherwise to improve their quality as amotor fuel or motor fuel component or petrochemical. Accordingly inaccordance with the practice of this invention a straight chainhydrocarbon fraction, cornparable to the desorbed straight chainhydrocarbons which are recovered during the desorption operation, andhaving a composition of about 23% by volume normal pentane, 56% byvolume normal hexane and 21% by volume normal heptane and exhibiting aresearch clear octane number of 39, was contacted with a platinumisomerization catalyst at a Itemperature inthe range 700-900 F., at apressure of about 500 p.s.i.g., at a space velocity of about 1.0v./hr./v., employing a hydrogen recycle rate of :about 4000 standard cu.ft. per bbl. charge. The resulting isomates were subsequently finishedyby removal of the straight chain hydrocarbons. The results obtained areset forth in Table IV.

TABLE IV Run No 1 l 2 3 l 4 Temp., F 750 S00 850 S00 Liquid RecoveryIsomate, wt 98.8 05. 9 95. 0 67. G

Do 98. 9 96. 0 95. 7 Isomate Oct. No., Res. Clear 45.0 C0. 0 75. 4 89. 6Isomate Oct. No., Res. Clear after finishing to remove straight chainhydrocarbons. S6 78.0 84

By operating in the .above-indicated manner substantially all of the`straight chain hydrocarbons in the initial 12 feed fraction are chargedto an improved high octane material or to branch chain hydrocarbons.

The practice of this invention is particularly applicable to catalyticreforming followed by finishing of the reformer effluent or reformatefor the removal of straight chain hydrocarbons therefrom. Petroleumfractions in the naphtha boiling range, eg. having an initial boilingpoint in the range 45-250" F. and an end point in the range -475 F. andcontaining a substantial amount of naphthenic hydrocarbons, for examplecontaining at least about 550% by volume naphthenic hydrocarbons, areparticularly `suited for treatment in accordance with this invention.

In accordance with another embodiment of the invention the catalyticreforming operation is carried out under relatively mild conditions oftemperature, pressure and throughput such that substantially only thenaphthenic hydrocarbons contained in the naphtha fraction undergoingtreatment are dehydrogenated during the catalytic reforming operationwhereas the remaining straight chain and non-straight chain (branchedacyclic and/or aromatic) hydrocarbons pass through the catalyticreforming operation substantially unchanged. By operating in accordancewith this embodiment of the invention the catalyst life of the catalystemployed in the catalytic reforming operation can be extended for anindefinite period of time. This is particularly advantageous when thecatalytic reforming operation employs an expensive platinum-containingnon-regenerable catalyst.

Further exemplary of the practice of this invention a catalytic reformednaphtha was finished in accordance with the practice of this inventionby the removal of the straight chain hydrocarbons therefrom. There wasprocured a high octane finished gasoline having an octane numbersubstantially greater than the initially charged naphtha and having avalue higher than that which could be economically reached by catalyticreforming alone. The results are indicated in Table V. Y

TABLE V Reformate Finished Charge Naphtha API 50` 3 5 ASTt ResearchOctane: 47

Clear 85. 9 92. 9 95.5 100. 0 2. 9 3.0

6 33 Percent Roc 98. 0 98.0 Yields, Vol. Percent:

Finished Naphtha.- Desorbed Material.

Still further exemplary ofthe practice of this invention a catalyticreformed gasoline was separated into ten' (l0) close Iboiling fractionsand finished by the removal of the straight chain hydrocarbonstherefrom.The results set forth in Table VI indicate that fractions of a catalyticreformed gasoline having a `boiling point above about 250 F. exhibit asmaller octane number increase than the lower boiling fractions.Accordingly it is advantageous to finish only the more responsive lowerboiling fractions of a reformate, leaving the relatively less responsivehigh boiling fractions untreated, rather than to finish the wholereformate.

i 13 TABLE v1 SELECTIVE FINISHING OF CLOSE BOILING FRACTIONS FROM ACATALYTIC REFORMATE [87.1 clear research oct] ASTM Res. Oct. ASTM Res.Oct. Boiling Vol. Per Clear +3 cc. TEL Cut No. Range, cent Cu- F.mulative Raw Finished Raw Finished For purposes of simplicity andclarity, conventional control equiprnent, valves, pumps, compressors,heaters, coolers, gas-liquid separators, fractionators, etc. have forthe most part not been illustrated in the drawing. The location andemployment of these auxiliary pieces olf equi-pment and the like in thepractice of this invention are Well known Ito those skilled in the art.Furthermore the abovedescribed operations of catalytic reforming,straight chain hydrocarbon adsorption and desorption and isomer-izationor reforming or converting of the desorbed straight chain hydrocarbonscan be carried out substantially continuously by employing a pluralityof catalytic reforming units 16 and adsorbers 2.9 and converters 51, oneor -rnore adsorbers 29 undergoing desorption-regeneration at the sametime. For purposes of simplicity and clarity only one reformer unit l16,one adsorber 29 and one converter 51 have been shown. The employment ofone or more of these units in the manner to effect substantiallycontinuous operation is Well known to those skilled in the yart.

As is evident to those skilled in the art many modiii'cations,substitutions and changes are possible in the practice of this inventionwithout departing from the spirit or scope thereof.

This application is a continuation-in-part of copending applicationSe-rial No.. 483,998, filed January 25, 1955 (now Patent No. 2,917,449),which in turn is a continuation-impart of application Serial No.478,426, now Patent No. 2,886,508, led December 29, 1954.

We claim:

1. A petroleum treating process which comprises catalytically reforminga petroleum naphtha to yield a reformate, subjecting said reformate tofractionation to separate therefrom a C., fraction, a light reformateiraction having -a boiling range in the range 75-250 F. and a heavyreformate fraction, contacting said light reformate fraction in theliquid phase with a Angstrom unit alumino-silicate molecular sieveadsorbent which selectively adsorbs straight chain hydrocarbons to thesubstantial exclusion of non-straight chain hydrocarbons to adsorbstraight chain hydrocarbons from said light reformate and to yield atreated light reformate substan- 14 tially free of straight chainhydrocarbons, blending the resulting treated light reformate with saidheavy reformate and at least a portion of said C., [fraction to yield aproduct having improved qualities as -a motor fuel.

2. A petroleum treating process which comprises catialytically reforminga heavy .naphtha to yield a catdytic reforrnate, fractionating saidcatalytic reformate to separate therefrom a C4 fraction, a lightrefor-mate fraction and a heavy reformate fraction, contacting saidlight reformate fraction with a 5 Angstrom unit aluminosilicatemolecular sieve adsorbent which selectively adsorbs straight chainhydrocarbons to the substantial exclusion of non-straight chainhydrocarbons to adsorb straight chain hydrocarbons therefrom,subsequently desorbin'g the adsorbed straight chain hydrocarbons fromsaid adsorbent, recovering from the aforesaid adsorption a treated lightreformate fraction and blending said treated light reforrnate `fractionwith said heavy reformate fraction.

3. A petroleum treating process which `comprises pretreating a broadboiling range sulfur-containing petroleum naphtha having lighthydrocarbon material boiling below F. and an end point -in the range 392to 475 F. to remove light hydrocarbon material boiling below "100 F. andto reduce the sulfur content of the remaining broad boiling rangenaphtha, catalytically reforming the pretreated broad boiling rangenaphtha, tfractionatin-g the reformate and separating hydrogen and lighthydrocarbons including C1 to C5 hydrocarbons therefrom, recycling aportion of said separated hydrogen to said reforming step, furtherfractionating and separating from the remaining reformate a lightreformate fraction having a boiling point not above about 250 F., and aheavy reformate fraction' having a boiling point range of about 250* to450 F., contacting said separated light reformate fraction With a 5Angstrom unit alumino-sili-cat-e molecular sieve adsorbent whichselectively adsorbs straight chain hydrocarbons to the substantialexclusion of non-straight chain hydrocarbons to Iadsorb straight chain'hydrocarbons therefrom, recovering from said adsorption operation atreated light naphtha [fraction now substantially free of vstraightchain hydrocarbons, blending said treated light naphtha fraction withsaid heavy refo-rniate to yield a product having improved qualities as amotor fuel.

4. A method in accordance with claim 3 wherein said light reformatefraction is contacted with said molecular sieve alumino-silicateadsorbent in the liquid phase.

5. A method in accordance with claim 3 wherein said light reformate'fraction is contacted with said aluminosilicate molecular sieveadsorbent inI the gaseous phase.

References Cited in the le of this patent UNITED STATES PATENTS2,493,499 Perry Jan. 3, 1950 2,818,455 Ballard et al Dec. 31, 19572,859,173 Hess et al. Nov. 4, 1958 2,888,394 Christensen et al. May 26,1959 2,891,902 Hess et al. lune 23, 1959 2,917,449 Christensen et al.Dec. l5, 1959

3. A PETROLEUM TREATING PROCESS WHICH COMPRISES PRETREATING A BROADBOILING SULFUR-CONTAINING PETROLEUM NAPHTHA HAVING LIGHT HYDROCARBONMATERIAL BOILING BELOW 100*F. AND END POINT IN THE RANGE OF 2 TO 475*F.TO REMOVE, LIGHT HYDROCARBON MATERIAL BOILING BELOW 100* F. AND TOREDUCE THE SULFUR CONTENT OF THE REFINING BROAD BOILING RANGE NAPHTHA,CATALYTICALLY REFORMING THE PRETREATED BROAD BOILING RANGE NAPHTHA,FRACTIONATING THE REFORMATE AND SEPARATING HYDROCARBON AND LIGHTHYDROCARBONS INCLUDING C1 TO C5 HYDROCARBONS THEREFROM, RECYCLING APORTION OF SAID SEPARATED HYDROGEN AND LIGHT REFORMING STEP, FURTHERFRACTIONATING AND SEPARATING FROM THE REMAINING REFORMATE A LIGHTREFORMATE FRACTION HAVING A BOILING POINT NOT ABOVE ABOUT 250* F., AND AHEAVY REFORMATE FRACTION HAVING A BOILING POINT RANGE OF ABOUT 250 TO450* F., CONTACTING SAID SEPARATED LIGHT REFORMATE FRACTTION WITH A 5ANGSTROM UNIT ALUMINO-SILICATE MOLECULAR SIEVE ADSORBENT WHICHSELECTIVELY ADSORBS STRAIGH CHAIN HYDROCARBONS TO THE SUBSTANTIALEXCLUSION OF NON-STRAIGHT CHAIN HYDROCARBONS TO ADSORB STAAIGHT CHAINHYDROCARBONS THEREFROM, RECOVERING FROM SAID ADSORPTION OPERATION ATREATED LIGHT NAPHTHA FRACTION NOW SUBSTANTIALLY FREE OF STRAIGHT CHAINHYDROCARBONS, BLENDING SAID TREATED LIGHT NAPHTHA FRACTION WITH SAIDHEAVY REFORMATE TO YIELD A PRODUCT HAVING IMPROVED QUALITIES AS A MOTORFUEL.